1. Technical Field
The present disclosure relates to a power amplifier and a transmission device which use a complementary metal-oxide semiconductor integrated circuit (CMOS-IC).
2. Description of the Related Art
An exemplary known power amplifier using a CMOS-IC is a switched capacitor power amplifier (SCPA) which achieves high efficiency (for example, see Sang-Min Yoo, Jeffrey S. Walling, Eum Chan Woo, Benjamin Jann, and David J. Allstot, “A Switched-Capacitor RF Power Amplifier”, IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. 46, No. 12, DECEMBER 2011). An SCPA which is a kind of class D amplifier performs amplitude modulation by changing the number of amplifiers switching between the power supply voltage and the ground (GND).
However, an SCPA of the related art fails to maximize the output power and the power efficiency. This problem will be described by using FIG. 1. FIG. 1 is a diagram illustrating an exemplary configuration of an SCPA of the related art.
In FIG. 1, the SCPA includes an output terminal 10, multiple capacitative elements (C) 11 to 15, and multiple amplifiers (AMP) 21 to 25. The capacitative elements 11 to 15 and the amplifiers 21 to 25 are disposed in such a manner as to be aligned in lines. In this configuration, the lengths of wiring from the amplifiers 21 to 25 to the output terminal 10 are different from each other. For example, the length of wiring from the amplifier 21 to the output terminal 10 is larger than that from the amplifier 23 to the output terminal 10. Therefore, the former wiring has larger parasitic capacitance and larger parasitic resistance. Accordingly, the output power and the power efficiency fail to be maximized.